|Summary:||[hwpmc] [patch] Loading hwpmc with an unknown cpuid causes a page fault in kernel mode.|
|Product:||Base System||Reporter:||Alan Somers <alans>|
|Component:||kern||Assignee:||freebsd-bugs (Nobody) <bugs>|
|Severity:||Affects Only Me||CC:||nicolas.masse|
Description Alan Somers 2012-01-09 23:20:12 UTC
Attemping to use hwpmc from a Xen guest on a Core i7 running in 64 bit mode, I got the following crash on bootup: xbd0: 20480MB <Virtual Block Device> at device/vbd/768 on xenbusb_front0 xbd0: attaching as ad0 Timecounter "TSC" frequency 2000036316 Hz quality 800 Fatal trap 12: page fault while in kernel mode cpuid = 0; apic id = 00 fault virtual address = 0x0 fault code = supervisor read instruction, page not present instruction pointer = 0x20:0x0 stack pointer = 0x28:0xffffffff81985b90 frame pointer = 0x28:0xffffffff81985c10 code segment = base rx0, limit 0xfffff, type 0x1b = DPL 0, pres 1, long 1, def32 0, gran 1 processor eflags = interrupt enabled, resume, IOPL = 0 current process = 0 (swapper) [ thread pid 0 tid 100000 ] Stopped at 0: *** error reading from address 0 *** db> where Tracing pid 0 tid 100000 td 0xffffffff8154f8b0 uart_sab82532_class() at 0 load() at load+0x39 syscall_module_handler() at syscall_module_handler+0xe6 module_register_init() at module_register_init+0xb0 mi_startup() at mi_startup+0x139 btext() at btext+0x2c The problem was that Xen changes the cpuid that guests see. Specifically, the result of do_cpuid(CORE_CPUID_REQUEST, cpuid) is changed to indicate that performance counters are not supported. Hence, pmc_core_initialize() returns EPROGMISMATCH. Eventually, that causes pmc_initialize() to execute a null function pointer at line 4692. Really, the root cause of the problem is that hwpmc isn't written very defensively. I've attached a patch that makes the panic go away, but doesn't make PMC work for my processor. Fix: ==== sys/dev/hwpmc/hwpmc_mod.c#2 (text) ==== @@ -4689,7 +4689,15 @@ if (md->pmd_pcpu_init) error = md->pmd_pcpu_init(md, cpu); for (n = 0; error == 0 && n < md->pmd_nclass; n++) - error = md->pmd_classdep[n].pcd_pcpu_init(md, cpu); + if (md->pmd_classdep[n].pcd_pcpu_init != NULL) + error = md->pmd_classdep[n].pcd_pcpu_init(md, + cpu); + else + printf("hwpmc: md->pmd_classdep[%d]." + "pcd_pcpu_init was not initialized. " + "This is a bug.\n" + "\tMost likely your CPUID is not " + "recognized by hwpmc.\n", n); } pmc_restore_cpu_binding(&pb); @@ -4882,7 +4890,15 @@ continue; pmc_select_cpu(cpu); for (c = 0; c < md->pmd_nclass; c++) - md->pmd_classdep[c].pcd_pcpu_fini(md, cpu); + if (md->pmd_classdep[c].pcd_pcpu_fini != NULL) + md->pmd_classdep[c].pcd_pcpu_fini(md, + cpu); + else + printf("hwpmc: md->pmd_classdep[%d]." + "pcd_pcpu_fini was not initialized." + " This is a bug.\n" + "\tMost likely your CPUID is not " + "recognized by hwpmc.\n", c); if (md->pmd_pcpu_fini) md->pmd_pcpu_fini(md, cpu); } How-To-Repeat: Compile an amd64 Xen domU kernel with the below lines in your configuration file and boot it: options HWPMC_HOOKS device hwpmc
Comment 1 Davide Italiano 2013-05-02 14:16:37 UTC
State Changed From-To: open->feedback Alan, some changes have been recently committed to HEAD, and the problem should be solved. I've not tested on Xen because I've not a machine with that available, but I was able to reproduce this same bug on VirtualBB. Do you mind to test if it also fixes the problem for you?
Comment 2 asomers 2013-05-03 21:49:55 UTC
Actually, I don't have a Xen machine anymore, either. Sorry.
Comment 3 Eitan Adler 2017-12-31 08:01:28 UTC
For bugs matching the following criteria: Status: In Progress Changed: (is less than) 2014-06-01 Reset to default assignee and clear in-progress tags. Mail being skipped